But to answer the question the question posed here, I'll provide several examples:

The Catch - In my estimation, this is probably the crème de la crème of all-time greatest plays in Crimson Tide history served up by Tyrone Prothro.

The Drive - T.J. Yeldon's catch against LSU, capping off an amazing late-4th-quarter drive in which the Tide had struggled all game offensively against the Bayou Bengals. Simply put, without this drive, and Yeldon's catch and run towards the endzone, the Tide do not make an appearance in the BCS National Championship game.

The Sack - In this play, Cornelius Bennett proves that he was the original Jadeveon Clowney, both rocking Notre Dame's Steve Beuerlein's world and taking the ball from him in the process. The play would forever be immortalized in the eyes of Tide fans by Daniel Moore's painting of the play, which can be seen at the end of the video.

The Goal Line Stand - In this Sugar Bowl was a matchup of two college football powerhouses, Penn State and Alabama, both ranked #1 and #2 respectively, that proved to be a defensive struggle throughout the entire game. However, what the game is most notably known for is Alabama's memorable goal line stand deep in the fourth quarter. After the stand, the Tide would go on to win, securing another championship for both the Crimson Tide, its tenth, and Bear Bryant, his fifth at the time.

The Strip - Another Sugar Bowl matchup, this time featuring the high-flying Hurricanes of Miami, number one coming into the matchup, and the Crimson Tide of Alabama, who were number two and coming off a highly-charged, emotional 28-21 victory over the Florida Gators in the inaugural 1992 SEC Championship game. However, in this game, the Hurricanes were the heavy favorites in this game, but the Tide were having none of that nonsense when they brought their heaving-hitting defense against the 'Canes, highlighted by George Teague's amazing strip of Miami's WR Lamar Houston. Though the play was negated by a defensive offsides by the Tide, it ultimately prevented the 'Canes by scoring, and served as a huge momentum shift and changed the tide (heh, puns are fun) of the game. Alabama would inevitably go on to win both the game and the national championship for the year of 1993.

Rocky Block (Credit goes to /u/isaymeh for bringing this one to attention) - Terrance Cody is known for many things among Tide fans during his stint at the Captstone: fat, charismatic and blocking two Tennessee field goals in the 2009's version of 'The Third Saturday in October'. The game was both highlighted by defensive competency and offensive ineptitude by both sides. However, the game will be remembered by Alabama's All-American DT, Terrance Cody, and his two field goal blocks, with the last one being both dramatic and controversial in fashion. The block, and thus the win, would preserve Alabama's 2009 dream season, which would culminate in Nick Saban's first national championship at Alabama, and the first for the Tide in 17 years.

Probably biased because I saw it happen right in front of me, but The Interception was pretty amazing. It's also known as The Play That Changed Football, because it's pretty likely that if Florida had won that game and Alabama had missed out on a National Championship, it would have had huge implications for the validity of the conference championship game format.

The best part of the strip is that Houston was "the fastest man to play football" and if he got it he was supposed to be gone. But then Teague catches him. It was like usain bolt getting beat in the 100m.